I am wandering what all extra is recommended if I get the sb-600. I know a diffuser but is there anything else that would be good to get to make it bettter, and is there any diffuser that is highly recommended if so can someone send me a link to it.
Recharable batteries. I'd get a good cheap diffuser. I got a $5 vinyl one here in Japan that works as well as any other I have ever seen. Other than that, couldn't think of anything else one would need.
I agree that a flash sync cord can be useful; however, I don't necessarily agree that it should be a SC-29. If you are using a body, like a D70, that has a built-in AF assist light, then you can turn off the AF assist light on the SB-600 and use the one on the body in a situation where you don't have the AF assist light on the flash pointed at the subject.
I recognize that many people prefer the AF assist light on the SC-29 to the built-in AF assist light on many camera bodies; however, you can pickup a used SC-17 on eBay for ~$25 if you are patient. A SC-29 costs about $75; so, you have to ask yourself if the AF assist light on the flash cord is worth the extra $50.
Although, a brand new SC-28 flash sync cord is only about $20 cheaper than a SC-29; so, if I were going to buy new then I might want to spend the extra $20 for a SC-29.
I don't have a SC-29 sync cord; so, I can't speak from experience; however, according to the SB-600 manual, the SB-600 includes the External AF-assist illuminator contacts; and, the SC-29 is listed as an optional accessory. It further states: "When using the SB-600 off-camera with the TTL Remote Cord SC-29, autofocus flash photography in dim light is possible because the SC-29 features an AF-assist illuminator function."